[DFTB-Plus-User] Treatment of Imaginary Frequencies

[Bálint Aradi]

Dear Ranajit,

I would guess, that those very low frequencies appear because of very 
small residual forces in the system. If all other frequencies (7 and 
above) are significantly higher, I won't probably worry about it.

Best regards,

Bálint

On 28.01.22 03:48, rsaha at icredd.hokudai.ac.jp wrote:
> Hello everyone,
> 
> I have a query about the small imaginary frequencies in the DFTB
> computations.
> 
> I am doing frequency (SCCTolerance = 1e-8 & RemoveTranslation = Yes)
> calculations after optimisation of the unit cells. The unit cells have ~
> 600 atoms. There are a few imaginary frequencies (as shown below for two
> different systems) that occurred which are very small.
> 
>   Vibrational modes (cm-1):
>      1   -1.46
>      2   -0.00
>      3   -0.00
>      4    0.00
>      5    7.40
>      6    7.41
> 
> OR
> 
>   Vibrational modes (cm-1):
>      1   -2.09
>      2   -1.02
>      3   -0.00
>      4    0.00
>      5    0.00
>      6    4.94
> 
> In this condition, should I need to remove these imaginary frequencies?
> 
> Thank you.
> Regards
> Ranajit
> 
> 
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-- 
Dr. Bálint Aradi
Bremen Center for Computational Materials Science, University of Bremen
http://www.bccms.uni-bremen.de/cms/people/b-aradi/

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